This invention relates to a process for making glycol ether acetates from acetic acid and a glycol ether. In particular, it relates to the use of a molar ratio of acetic acid to glycol ether of about 1.1 to about 2 and to the use of butyl acetate or dibutyl ether as an azeotropic agent.
Glycol ether acetates are generally manufactured by esterifying an ethylene glycol ether with acetic acid. To force the reaction to completion, the water by-product formed is removed using an agent that forms an azeotrope with water, known as an azeotropic agent or an entrainer. When the azeotrope is condensed, the entrainer must separate from the water so that the entrainer can be recovered and recycled.
Historically, toluene was used in industry as the entrainer. However, toluene is now regarded as a health hazard due to its toxicity, and tighter restrictions on the use of toluene have prompted manufacturers to replace it with hydrocarbons such as octane. Octane, however, does not work well for this system because, for unknown reasons, it carries over large amounts of the reactants (i.e., the glycol ether or acetic acid) with its water azeotrope, which then enter the waste water stream. This carryover can be as high as 30 wt % for acetic acid and 20 wt % for glycol ethers. The water often can be so contaminated with organics that its flash point is too low for safe handling, further increasing the disposal cost. Of course, this loss of raw materials significantly adds to the cost of manufacturing the acetate. Other water azeotrope solvents, such as p-xylene, ethyl benzene, 1-octene, heptane, and cyclohexane, for unknown reasons carried over at least 10 wt % organics no matter how the process conditions, such as the reflux ratios, were adjusted and they were much poorer entrainers.